(1) Field of the Invention
The present invention relates to a reader-printer, particularly to a reader-printer with an image size judging function.
(2) Description of the Prior Art
On a microfilm, images of different sizes, for example, A3 size and A4 size, are recorded in the same magnification. In printing an image recorded on such a microfilm, it is necessary to select a paper feeding cassette of a size of the image. This requires judgment of the image size.
A conventional reader-printer with an image size judging function is disclosed in Japanese Patent Publication Kokai No. 61-165746. This reader-printer utilizes the transparency difference between an image and a blank portion present between the adjacent frame images. It also utilizes the difference between the position of the blank portion when a small size (for example, A4 size) frame image is at an exposure position and that when a large size (for example, A3 size) frame image is at the exposure position. A sensor is provided to detect the blank portion, for example, when the small size frame image is at the exposure position. Accordingly, when the sensor detects the blank portion, the image is judged to be of small size, and when not, the image is judged to be of large size, which enables selection of a paper feeding cassette.
This type of reader-printer, however, has the following problems.
That is, in retrieving frame images, positions at which the blank portion is stopped is subtly varied since a film carrier does not always stop at exactly the same position, even if all the images are of the same size. Therefore, in order to enable detection of the blank portion regardless of the various stopping positions, the image size judging sensor is required to have a large detection area. However, width of the blank portion is not fixed and high detection accuracy cannot be obtained in detection of the narrow blank portion, apart from the case of the wide blank portion. This may cause an incorrect judgment.
Further, the image size judgment must be made prior to a printing operation because it is utilized in selecting a paper feeding cassette. In order to meet this requirement, the judgment may be made in the reader mode. However, this entails the problem that the shadow of the sensor is seen on the screen when the sensor is illuminated by light.